The present invention relates to machines for processing mixed recyclable materials, and more particularly, to disc screen apparatus suited for separating paper from a stream of mixed recyclable materials.
Material recycling has become an important industry in recent years due to decreasing landfill capacity, environmental concerns and dwindling natural resources. Many industries and communities have adopted voluntary and mandatory recycling programs for reusable materials. Solid waste and trash that is collected from homes, apartments or companies often combine several recyclable materials into one container. When brought to a processing center, the recyclable materials are frequently mixed together in a heterogenous mass of material. These mixed recyclable materials include newspaper, magazines, mixed paper, cardboard, aluminum cans, plastic bottles, glass bottles and other materials that may be recycled.
Disc apparatus or xe2x80x9cdisc screensxe2x80x9d are increasingly used to separate streams of mixed recyclable materials into respective streams or collections of similar materials. This process is referred to as xe2x80x9cclassifyingxe2x80x9d, and the results are called xe2x80x9cclassificationxe2x80x9d. A disc screen typically includes a frame in which a plurality of rotatable shafts are mounted in parallel relationship. A plurality of discs are mounted on each shaft and a chain drive commonly rotates the shafts in the same direction. The discs on one shaft interleave with the discs on each adjacent shaft to form screen openings between the peripheral edges of the discs. The size of the openings determines the dimension (and thus the type) of material that will fall through the screen. Rotation of the discs, which have an irregular outer contour, agitates the mixed recyclable materials to enhance classification. The rotating discs propel the larger articles which are too big to fall between the discs across the screen. The general flow direction extends from an input area where the stream of material pours onto the disc screen to an output where the larger articles pour off of the disc screen. The smaller articles fall between the discs onto another disc screen or a conveyor, or into a collection bin.
There is a substantial market for recycled newspaper. Therefore, it is important that any disc screen which is designed to classify mixed recyclable materials be capable of thoroughly separating newspaper from the heterogenous mass of material. Prior disc screen apparatus designed to handle a stream of mixed recyclable materials have included multiple overlapping disc screens with different angles of inclination and different sizes of openings between the discs. They are capable of separating broken glass from containers. They are also capable of separating mixed paper and newspaper from the stream of mixed recyclable materials. These apparatus can be tilted at various angles to improve the efficiency of separation. However, a consistent problem that has been encountered with disc screen apparatus that is used to classify mixed recyclable materials is the fact that newspaper sometimes rolls into a clump or mass midway up the final disc screen and will not be ejected off of the upper terminal end thereof If the angle of inclination of the final disc screen is reduced, then containers and bottles will be undesirably conveyed up the final disc screen and off of its discharge end. This problem is exacerbated where the newspaper is wet or damp.
Most disc screen apparatus that have been developed for classifying mixed recyclable materials have used a flat, generally planar disc screen. The stream of mixed recyclable material is conventionally deposited toward the lower end of the screen along a conveying direction which is generally perpendicular to that of the shafts. The screen is typically inclined and much of the material swirls at the location of deposit. Paper tries to move upwardly as containers try to roll rearwardly and this conflict in flow directions inherently limits the throughput of the screening apparatus. The efficiency of the classification process is also significantly impeded by this conflict in flow directions. Furthermore, it has sometimes been necessary to install multiple blowers along the relatively wide lower end of the disc screen in order to prevent paper from falling off the same.
In accordance with the present invention a disc screen apparatus has a V-shaped configuration with a lowermost region that provides a laterally inclined trough that receives the mixed recyclable materials. Broken glass falls downwardly between the discs of the lowermost region. Large articles, such as plastic milk bottles and soda pop containers, tumble down the trough and eventually fall off its lower end. Newspaper is conveyed upwardly over the terminal upper ends of a pair of vertically inclined regions of the disc screen apparatus. In the preferred embodiment, the frame of the disc screen apparatus incorporates ducting for connecting a source of pressurized air to one or more air manifolds that blow air toward the vertically inclined regions of the disc screen apparatus for helping the discs in these regions convey newspaper up the inclined regions and over their upper ends. The angle of inclination of the vertically inclined regions is preferably adjustable with a lifting mechanism in order to optimize the efficiency of classification of the V-shaped disc screen apparatus.